Dual air particle sample cassette and methods for using same

ABSTRACT

An air particle sample cassette enables concurrent or sequential collection of air particle samples. The dual air particle sample cassette has top and bottom covers that fit together to provide an airtight seal between them. The airtight seal may be provided by adhesive or otherwise. However, a close fit between the two also aids in obtaining an airtight seal. The top cover has tapering inlets circumscribed by channels. The inlets taper to create increased air speed at the exit slit of the inlets. The inlets have rounded tops for greater collection of air and the circumscribing channels provide means by which plastic caps or otherwise may be used to protect the inlets from collecting air until desired. The sample plate or collecting slide is fitted to the bottom of the top cover and obstructs the direct flow of air to the exit port. The collecting slide is protected from contact with other cassette elements by spacers or sidewalls which generally leave the corners of the bottom cover open. The exit port enables the common application of vacuum pressure to draw air through the inlets. Different inlet characteristics or air speeds may serve to enable selection of size of the particle sampled. Filter elements may also be introduced upstream of the inlets to further select sample particle size.

This application is a divisional of application Ser. No. 10/875,095,entitled Dual Air Particle Sample Cassette, filed on Jun. 22, 2004 andnow U.S. Pat. No. 7,155,988 which application is commonly assigned andherein expressly incorporated by reference.

COPYRIGHT AUTHORIZATION

Portions of the disclosure of this patent document may contain materialwhich is subject to copyright and/or mask work protection. The copyrightand/or mask work owner has no objection to the facsimile reproduction byanyone of the patent document or the patent disclosure, as it appears inthe Patent and Trademark Office patent file or records, but otherwisereserves all copyright and/or mask work rights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to air particle sampling cassettes and devices,and more particularly to a dual air particle sample cassette thatenables one or more samples of air to be taken at a time by the samevacuum sources.

2. Description of the Related Art

Air sampling has become an important aspect of safety and healthconcerns due to the rise of the present day industrial economy.Additionally, certain health aspects of individuals are better addressedwhen the pollen and/or particulate count of the surrounding area isknown.

With respect to industrial processes and the like, chemical processesare often used in industries that produce substances that are generallynot found in nature. Many of these are toxic and must be monitored inorder to prevent injury, sickness, disease, or even death in individualsthat might be exposed to such substances. Some of these substances arevery potent and act very quickly while others require longer periods oftime in order to have their deleterious effect. By monitoring orsampling the air, quantitative evaluations can be made upon suchsubstances in the air.

With respect to people who have allergies, the pollen, mold, dust, andother particulates becomes important as their health is directly (andusually adversely) affected by the increase in such substances. Byproviding means by which such particulates can be detected, anindividual allergic (or a community thereof) is better prepared toaddress the environmental conditions.

Other uses and applications for air samplers and the informationdelivered by them arise in a variety of circumstances. Certainbiological, botanical, and other endeavors may benefit from anunderstanding of the air quality in certain areas. To this extent andotherwise, air sampling systems have arisen in the art to provide meansby which quantitative information regarding air quality can be obtainedby direct sampling of the air.

As set forth in U.S. Pat. No. 5,693,895 issued to Baxter on Dec. 2, 1997for a Versatile Airborne Particle Impaction Sampler, obtaining accuratesamples of airborne particles such as fibers, pollen, mold spores,insect parts and other bioaerosols is necessary or desirable for anumber of different purposes. Environmental professionals have a need todetermine the presence and quantity of deleterious particles such asasbestos fibers in the air. Aero-biologists and allergists need toidentify and quantify airborne pollen and mold spore concentrations forpatient diagnosis. Epidemiologists are concerned with particles carryingbacteria, such as that responsible for Legionnaire's Disease, inair-conditioning systems and the like.

An increasing need for more versatile, convenient and effectiveapparatus for sampling airborne particles has developed in such areas asenvironmental air quality monitoring, fire and flood restoration, andindustrial and occupational monitoring.

Filter sampling has long been used for particle and fiber analysis. Airis drawn through a micro porous filter of the sort marketed byMillipore, Nuclepore and other companies. The filter is then examinedunder a microscope to determine the type and concentration of particlestrapped on the filter media.

While effective for some purposes, filter sampling requires longsampling times to obtain reliable detection limits. The large filterareas require slow, careful examination by the microscopist performingthe analysis. Relatively large filter areas, typically about 385 to 900mm², are normally required to balance high sample flow rates, requiredvelocity and resulting back pressures. Large particles such as pollenoften do not remain attached to the filter, separating there from duringtransportation and handling. Further, special stains and refractiveindex liquids required to assist in particle identification are oftenincompatible with the filter media.

Slit or impact samplers, which direct air at relatively high velocitythrough a narrow rectangular slit against a tacky material, have anumber of advantages over filter sampling. A sample sufficient foranalysis can be obtained in minutes rather than hours, the area to beexamined is much smaller (approximately 16 mm²) than the areas providedwith filters and the tacky nature of the material used to collect thesample will retain large particles better than filters. Present slittype samplers are assembled in a housing containing a vacuum pump, aholder for a slide coated with a tacky material, such as a suitablegrease, with a narrow rectangular slot in the housing adjacent to thetacky surface.

These devices can only be used in an upright or fixed position andcannot be easily used in confined or restricted spaces such asventilation ducts because of their relatively large size. Electricity topower the vacuum pump must also be run to the sampling site, or abattery power source in the housing must be provided which furtherincreases the bulk of the unit. These units are not weatherproof and aredifficult to use in moist or exposed areas. Dust contamination can buildup inside the case resulting in cross contamination of sample slides andwill require regular and extensive cleaning between sample collectionepisodes. Further, slit geometry in prior collectors is such as tocollect the undesired less than about 2 μm particles, making examinationand analysis more difficult.

Upon completion of sampling, the slides must be removed from thesampling device, packaged and shipped for analysis. Users must havespecialized knowledge of sampling, decontamination, shipping andanalysis procedures. Still, the opportunity for contamination, eitherinadvertent or intentional, is great.

With patients in hospitals, allergic persons while sleeping, workers inconfined environments, etc. often have need for sampling near theirfaces to determine their actual exposure to allergens, toxic materials,etc. The large sampling devices of the prior art are very inconvenientfor such uses, in particular where the person is mobile, because oftheir lack of easy portability.

Prior attempts have been made in the art with respect to sample cellsand cassettes for air sampling systems and otherwise. Brief descriptionsof such prior attempts are set forth below. While the descriptions arebelieved to be accurate, no admission is made by them regarding theirsubject matter which is solely defined by the patent or referenceinvolved.

Typical of prior particle collection devices are those described byBerger in U.S. Pat. No. 4,725,294 and Leith in U.S. Pat. No. 5,304,125.The Berger device uses a single, round nozzle that will produce acircular, gradually decreasing spot of collected particles that is muchmore difficult to analyze than a narrow line of particles and will tendto collect sub-micron particles that obscure the larger which are to beanalyzed. Leith discloses a device using four spaced slits that aresimple slots in a thin plate, which will not discriminate between largerparticles of interest and sub-micron particles that are not of interest.

The Baxter U.S. Pat. No. 5,693,895 discloses a single collector having aslide that is supported by the bottom ledge of the cell base.

The Marple et al. U.S. Pat. No. 4,827,779 discloses a personal airsampling impactor having a single vacuum source, multiple inlets, and ina separate embodiment, separate collection surfaces on the impactorplate.

The Marple U.S. Pat. No. 4,133,202 teaches a single stage impactor forsampling breathable aerosol particles having a nozzle plate withmultiple different sized nozzles for allowing different sized particlesthrough and an impactor unit with a plurality of particle collectingsurfaces.

The Basch et al. U.S. Pat. No. 5,553,507 shows an airborne particulatesampling monitor having multiple intakes, each with its own filter unit,and a single vacuum source. The Shih et al. U.S. Pat. No. 5,702,506teaches an aerosol size selecting sampling device having multiple inletswith pre-filters and a single vacuum source.

Van Den Wildenberg U.S. Pat. No. 6,342,388 discloses an apparatus forcollecting airborne bacteria through impaction having multiple inletsand a single vacuum source.

The Sugita et al. U.S. Pat. No. 6,565,638 discloses a device forcollecting air-borne micro-organisms having multiple nozzle openings anda single vacuum source.

The Jordan, Sr. et al. U.S. Patent Application Publication No.2003/0075048 discloses a particle collection unit for separatingparticulate matter from a gas flow having an adhesive collecting member.

The Brixius et al. U.S. Pat. No. 3,898,161 discloses an air filtrationdevice having a color-coded filter. Refer to column 4, lines 10-12.

The Miller et al. U.S. Pat. No. Des. 422,071—illustrates a partitionedfilter element.

The Ayers published international application no. WO 03/002981—teaches adevice for collecting and measuring particulate matter from a stream ofair using two or more inlets each being selective as to the size of theparticle able to pass through the inlet.

Despite the development of prior devices, the art may still be improvedby a dual or multiple inlet air particle sample cassette that providesconvenient means by which air may be sampled.

SUMMARY OF THE INVENTION

In view of the foregoing disadvantages inherent in the known types ofair sampling devices now known in the prior art as well as theadvantages of furthering the art with respect to such air samplingsystems, the present invention provides a new air particle samplecassette that provides at least two inlets such that air samples can betaken concurrently, sequentially, episodically, or otherwise by means ofa disposable or reusable air sample cassette.

The general purpose of the present invention subsequently described ingreater detail below is to provide an air sampling system that enablesmultiple samples to be taken either at the same time or at differenttimes as multiple inlets transmitting air to isolated chambers provideseparate and independent air particle sampling systems in a tandem ormultiple package for better, more consistent, or more convenient airparticle sampling, the cassette not anticipated, rendered obvious,suggested, taught, or even implied by any of the prior art air samplingsystems or devices, either alone or in any combination thereof.

In the present invention, the dual air particle sample cassette has atop half and a bottom half which fit together to provide a sealedenclosure in which air samples are obtained. The top half of the airsample cassette has a pair of inlets of generally square or rectangularin nature that taper into corresponding narrow slots so that a volume ofair is rapidly accelerated to a significantly high velocity by means ofthe Venturi effect or otherwise. This high velocity air carries anyparticulate materials with it which are also subject to acceleration andincreased velocity.

An obstructing sample collection plate is present in front of each slitopening in order to obstruct the direct path of the air and particleflow. A sample plate is held in place at the bottom of the top cover andis spaced apart and away from the narrow slit opening. This enables thesample plate to travel with the inlets. The sample plate defines acollection area in front of each narrow slit with each collection areaisolated and separate from all other collection areas. The sample platedoes not fully enclose the collection area, but a gap at the edge of thecollection plate is present between itself and the bottom sidewalls ofthe top cover to allow the escape of air and any particles not collectedby the tacky medium present on the surface of the sample plate. Apartition or rib separates the individual collecting areas or chambersof the top cover by contact engagement with the sample plate.Consequently, airflow cannot occur between the areas in front of theslit inlets to the collecting area at the tapered ends of the inlets ofthe top cover.

The air then travels through this gap and onto the interior of thebottom cover where a nozzle or outlet is subject to vacuum pressurewhich pulls the air through the cassette and the tapered top inlets ofthe top cover.

The bottom cover has a well, reservoir, or other receiving area for thebottom portion of the top cover. Ledges, supports, or spacers arepresent at the sides of the well, but are absent from the corners inorder to allow air to pass through or otherwise. The air passing throughthe sample plate gap travels through and about the enclosed area definedbetween the top and bottom covers and out the vacuum nozzle.

Legs, support, or spacing elements may be present at the eight corners(4 top, 4 bottom) of the cassette. These legs or supports may enableeasy engagement in air sampling system by the cassette.

Generally, one sample plate or collecting slide may be fixed in placeonto the top cover with no sample contamination occurring betweencollection areas as the sampling areas are separated by at least onepartition. The inlets may be shaped to efficiently sample differentparticle sizes, including 5 μm particles and 20 μm and larger particles.The cassette may have two identical inlets as might be used for a 5 μmparticle collection or two different nozzles with one for 5 μm andanother for 20 μm particle sampling, for example. Only a single exitvacuum port is present in the cassette so that one vacuum source isneeded for either concurrent or sequential particle collection.

The sample plate or collecting slide has tacky material on its topfacing the narrow slit of the inlet for nonviable particle sampling orthe collecting slide may have biocompatible media for viable sampling.Alternatively, one side or collecting area may have tacky material fornonviable particle sampling and the other side may have tacky media forbiocompatible for a viable sampling.

When delivered to the customer or user, the inlets may be covered withtamper proof tape and/or removable and/or replaceable cap. The cap maybe made of plastic.

The collecting slides sample plate may be coded to correspond with acertain select inlet for permanent sample identification. The collectingslide sample plate may be configured with a filter for sampling bothviable and nonviable particles. Additionally, a disposable filter screenmay be fitted onto one or more of the inlets to remove debris in the airbefore it is sampled.

In one embodiment, an air particle sample cassette receives a sampleplate to sample air. The cassette has a plurality of inlets with eachinlet having a tapering cross section with a first opening wider than agenerally oppositely opposed second opening. The second opening leads toa recess that has sidewalls and a rib, the recessed portion capable ofreceiving a sample plate. The rib separates at least two of the secondopenings and prevents gas flow between them when the sample plate ispositioned over the recess. The sidewalls establish a gap with thesample plate when the sample plate is positioned over the recess. Abottom cover has vacuum aperture and removably encloses the recess. Whena vacuum is applied to the vacuum aperture, air is pulled through atleast one of the second openings to collide with the sample plate.Matter in the air is collected by the sample plate as it obstructsdirect flow of the air to the vacuum aperture and guides the air to thegap.

Upon collecting matter from the air for a certain period of time orotherwise, the sample plate is inspected and/or analyzed for thecollected matter. The quality and/or contents of the air can then beanalyzed for health, safety, and/or other purposes.

In another aspect of the invention, there is disclosed a method ofobtaining multiple air samples using a single air sampling device whichcomprises a cassette including a first inlet and a second inlet. Theinventive method comprises steps of:

a) drawing a first sample of air through one of the first and secondinlets;

b) collecting particulates contained in the first sample of air;

c) drawing a second sample of air through a second one of the first andsecond inlets, wherein the second sample of air is sealed and separatedfrom the first sample of air; and

d) collecting particulates contained in the second sample of air.

In certain circumstances, steps a) and c) above occur simultaneously,while in other circumstances, they occur sequentially. Additionally, insome situations, steps a) and b) occur in a different location thansteps c) and d), while in other situations steps a) and b) occur in asame location as steps c) and d). A sample slide is disposed in thecassette for performing the collecting step b) and d).

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an air-samplingdevice.

It is another object of the present invention to provide a dual airparticle sample cassette.

It is yet another object of the present invention to provide an airsampling system that has multiple chambers isolated and separated fromone another so that independent samples may be taken through selectableoperation of the corresponding inlets.

It is yet another object of the present invention to provide adisposable air sample cassette that can take multiple air samples.

It is yet another object of the present invention to provide an airsample cassette for taking multiple air samples either concurrently andsimultaneously, or sequentially, or intermittently.

These and other objects and advantages of the present invention will beapparent from a review of the following specification and accompanyingdrawings. The foregoing objects are some of but a few of the goalssought to be attained by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded side perspective view of the dual air particlesample cassette of the present invention with the top cover spaced apartand above the bottom cover.

FIG. 2 is a side perspective view of the dual air particle samplecassette of FIG. 1 showing the top and bottom covers fitted together.

FIG. 3 is a longitudinal cross sectional view of the assembled dual airparticle sample cassette of FIG. 2 taken along line 3-3 thereof.

FIG. 4 is a side cross sectional view of the dual air particle samplecassette of FIG. 2 taken along line 4-4 thereof through the channelbetween the two inlets.

FIG. 5 is a side cross sectional view of the dual air particle samplecassette of FIG. 2 taken along line 5-5 thereof through the left inletand showing the cross section thereof and its tapering nature.

FIG. 6 is a side perspective view of the dual air particle samplecassette of FIG. 2 with a filter cap in a raised position and a regularcap in a fitted position.

FIG. 7 is a side perspective view of the dual air particle cassette ofFIG. 6 with both caps fitted and the cassette sealed with tape.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The detailed description set forth below in connection with the appendeddrawings is intended as a description of presently preferred embodimentsof the invention and is not intended to represent the only forms inwhich the present invention may be constructed and/or utilized. Thedescription sets forth the functions and the sequence of steps forconstructing and operating the invention in connection with theillustrated embodiments. However, it is to be understood that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

Referring to the drawings where like new numerals of reference designatelike elements throughout it will be noted that the dual, or multiple,air particle sample cassette 100 of the present invention has a topcover 102 and a bottom cover 104. While FIG. 1 is an exploded of thecassette 100, FIG. 2 shows an assembled portrayal of the cassette 100with the top 102 and bottom 104 covers are fitted together to generallyform an airtight seal that may be secured by tape, adhesive, orotherwise (not shown).

The top cover 102 has inlets 110 and 112. The inlets 110, 112 may beidentical or they may be different. By appropriate selection of thedifference between the two inlets 110, 112, samples can be taken ofdifferent particles. Such differences may include the angle of taperingor the width of the slit at the end of the inlets. Additionalcharacteristics of the inlets may be altered during manufacture orotherwise to achieve performance characteristics that are desirable forthe circumstances of the air sampling the cassette 100 is to perform.

The inlets 110, 112 are surrounded by a channel 114 that circumscribesthe inlets and passes between them as well. The channel may allow foreasier connection to the inlets 110, 112 by caps, covers, conduits,hoses, or otherwise (not shown).

The tops 116 of each of the inlets 110, 112 may be tapered on theinterior portion of the inlet but flat on the exterior portion thereof.The tapering of the top 116 of the inlets 110, 112 may provide forgreater distribution of the vacuum applied to the cassette 100. Theinlets 110, 112 thereby have additional “purchase” on the surroundingair to gather such air from the greater area or cross section. If theinteriors 118 were not tapered at the tops 116 thereof, the air would begathered from a smaller cross section than may be available with taperedtops 116. The inlets 110, 112 only gather air at their top and the airtaken in generally has a velocity in the direction of the inlet. Bytapering the tops 116, those velocities and directions are made througha wider angle than would be achieved with flat or sharp angular tops116.

The bottom portion 130 of the top cover 102 has a circumscribingsidewall 132 which is discontinuous at its bottom-most edge. Thesediscontinuities 134 show as gaps between certain descending elements ofthe circumscribing sidewall 132. Central posts 136 provide lower supportfor the top cover 102 and help prevent the bottom cover 104 fromengaging the sample plate or collecting slide 140 (FIGS. 3-5). Byfitting within the circumscribing sidewall 132 and the central posts136, the sample plate-collecting slide 140 is recessed within the bottom130 of the top cover 102.

As shown in FIGS. 4 and 5, the sample plate 140 does not extendcompletely across the width of the bottom of the top cover 102, althoughthe sample plate preferably does extend the length of the bottom.Instead, a small gap 142 is present between the adjacent sidewall 132 orpost 136 and the sample plate 140. This allows air to travel over andacross the sample plate 140 before exiting out through the gap 142 andinto the bottom cover 104. Without the sample plate, the air comingthrough the inlets 110, 112 travels straight and onto the bottom cover104 without having an opportunity to leave any suspended or colloidalparticulates on a collection device such as the sample plate 140.

The sample plate 140 requires the accelerated air to impact the sampleplate. As the particulates carried by the air have more mass, they havea corresponding greater momentum and inertia. While such particulateswill generally have the same speed and velocity as the air emerging fromthe inlet slot/slit 178, the particulates will not change theirdirection as quickly as the surrounding air. Instead, the particulates(which are significantly more massive than the surrounding airmolecules) will change direction more slowly than the surrounding airwhen the incoming air encounters the sample plate 140. While the airwill have a tendency not to stick to any medium present on the surfaceof the sample plate 140, the particulates will have a greater tendencyto embed themselves or stick to such medium. Not only does the greatermomentum of the particulates account for this, but once particulates docontact media, the greater surface area of the particulates allow forgreater engagement of such media.

As seen in FIG. 1, the bottom cover 104 generally has a circumscribingouter wall 150 which fits about the circumscribing sidewall 132 of thetop cover 102 when the two are fitted together as shown in FIG. 2 or thelike. Preferably, generally airtight seal is formed between the innerportion of the circumscribing outer wall 150 of the bottom cover 104 andthe outer surface of the circumscribing sidewall 132 with the top cover102. An airtight seal may also be ensured by adhesive between the twowalls 132, 150, airtight tape surrounding the seam between the top andbottom covers 102, 104 or otherwise. It is generally most advantageousto have an airtight seal between the two cover portions 102, 104 as thevacuum that is pulled upon the vacuum nozzle 152 should be transmittedexclusively to the inlets 110, 112 to ensure control over the airsampled by the cassette 100.

The bottom cover 104 has side ledges/supports/spacers 154 at theintersection between the horizontal bottom 156 and the verticalcircumscribing outer wall 150. These ledges 154 serve to support the topcover 102 by engaging the circumscribing sidewall 132, the central posts136, or otherwise. Despite the presence of the circumscribing sidewall132 and the spacers/ledges 154, an airtight seal is preferable betweenthe top and bottom covers 102, 104. Defined in the bottom 156 of thebottom cover 104 is an aperture 158 generally centrally located in thebottom 156 of the bottom cover 104. The aperture 158 leads to the vacuumnozzle 152 and serves as means by which any vacuum pulled upon thevacuum nozzle 152 is transmitted to the cassette 100 and the inlets 110,112. As shown in FIGS. 3-5, the vacuum nozzle 152 may be tapered at itsend 160 to aid in the application or connection of a vacuum hose or thelike.

Both the top and bottom covers 102, 104 have outwardly extending legs170 which may serve to help assemble and disassemble the cassette 100 aswell as providing additional advantages such as protecting the inlets110, 112 and/or the vacuum nozzle 152 so they do not stand too proud orextend too far outwardly from the central and generally flat portion ofthe cassette 100.

As shown in FIG. 3, a central rib 172 may be attached to or conjoinedwith the sample plate 140 by adhesive or otherwise to separate the twoor more recessed areas 174 defined by the circumscribing side wall 132as well as a spacing support ledge 176 circumscribing or otherwise theinterior of the bottom 130 of the top cover 102.

The height of the central rib 172 and the spacing support ledge orledges 176 define the distance between the narrow inlet slot 178 (FIG.5) and the sample plate/collecting slide 140. This distance between thesample plate 140 and the narrow inlet slot 178 defines how much distancethe air travels upon exiting the narrow inlet slit 178. As the path ofair travel (FIGS. 3 and 5) is initially towards the sample plate 140 andthen to the gap 142, it is most desirable to have the sample plate 140collect as much particulate matter as is possible before the air exitsthe associated recessed area 174. Therefore, the distance between thenarrow inlet slot 178 and the sample plate 140 should be as great aspossible to allow maximum air flow but as small as possible to preventparticles from traveling with the air and not impacting the tacky oradhesive substance(s) present on the top of the sample plate.Correspondingly, the viscosity of the fluid, in this case air, travelingthrough the narrow inlet slot 178 may be a determining factor as far asthe spacing between the narrow inlet slot 178 and the collecting plate140. In one embodiment, the recessed gap distance 180 may be on theorder of 0.5 mm to 15 mm. For low-density gasses, or for high viscosityfluids, other distances may be preferable.

Additionally, in FIG. 5, a gap present between the sample plate 140 andthe circumscribing wall 132 may be present to allow passage from theplenum area, or recessed area 174 of the top cover 102 to the lowerplenum space 198 of the bottom cover 104. This side gap 210 allowspassage of air from the top cover 102 to the bottom cover 104. As isseen in FIG. 5, such a gap is necessary for solid or impermeable sampleplates 140 such as glass slides or the like. However, on the right sideof FIG. 5, no gap is present for a permeable sample plate 140 such as afilter media or the like. The gap distance may be on the order of 0.5 mmto 2.0 mm or similar. The plenum spaces 174, 198 may have heights on thesame order or larger.

Additionally, the width of the narrow inlet slot 178 may be selectablychosen during manufacture or otherwise to determine the speed at whichthe air passes through the narrow inlet slot. In some embodiments, anair speed of approximately 35 miles per hour enables the collection of 5μm particles on a selectable basis. For other embodiments, an air speedof 3.5 miles per hour generally selects for particles of 20 μm size. Thedual air particle sample cassette 100 may use a snap fit clip orotherwise in order to obtain the snug fit between the top cover 102 andthe bottom cover 104. The dual air particle sample cassette 100 forms asingle, and possibly disposable unit for sampling the air particles in apredictable, reliable, and quantitative fashion. The cassette 100enables the collection of two (2) air samples on a single collectingsheet 140. When the collecting sheet 140 is sent to the lab for handlingand processing, both samples may be processed at the same time with verylittle risk of cross contamination between the two.

The top cover 102 is configured with two inlets 110, 112. The inlets areconfigured so that when a vacuum is drawn that pulls air through thenarrow inlet slot 178, the tapering nature of the inlet createssignificant air velocity at the narrow inlet slot 178 and past thesample plate 140. Various inlet configurations may be embodied in thecassette 100. Generally, air velocity determines the size of theparticles that are sampled by the sample plate 140. The top cover 102may have more then two inlets 110, 112. Indeed, configurations havingthree inlets, four inlets, or more may be possible. The rounded radialnature at the top 116 of the inlets 110, 112 may enable better aircollection and sample results.

The central rib 172 separates the sample collecting areas into two ormore compartments. Where more than two sample compartments 174 arepresent, additional ribs 172 may be required. Such ribs 172 preventmixing or contamination between the multiple samples.

The bottom cover, or base, 104 has a single exit port 152 in the form ofa vacuum nozzle 152. The use of a single vacuum source for both or allsamples enables both concurrent sampling or sampling via one inlet andone sample compartment 174 at a time.

The dual air particle sample cassette 100 may collect and evaluateairborne fungi including viable and nonviable spores. The tacky materialon the collecting slide 140 below the slit 178 may be present fornonviable sampling. A filter media can be used for viable sampling. Asticky filter media can be used for both viable and nonviable sampling.

Such filter media may include a variety of thin filters that optionallyhave an underlying support media. Some filter media may not requiresupporting substrates or the like to function well. In FIG. 3, a hybridsample plate/collecting slide 140 is shown where the right side 190 ofthe slide 140 may be glass or some other flat surface that can betemporarily fixed to the top cover 102 via adhesive 192 present alongthe central rib 172. On the left side 194 of FIG. 3, filter media isshown that, instead of allowing air to pass around the filter media 196,the air or other gas passes through the filter media 196 and anyparticulate matter (according to the selection size of the filter media196) is trapped in the filter media 196.

The filter media 196 may be any of a variety of materials in whichparticles above certain size may be trapped while particles below acertain size are allowed to pass through. In this way, a variety offilters can be constructed that selectively trap particles of certainsizes. The filter media should be sufficiently thin so that it fitswithin the spacing support ledge 176 of the bottom 130 of the top cover102. The plenum space 198 generally between the sample plate 140 and thebottom 156 of the bottom cover 104 should be left open for the free andclear travel of air or other fluid there through.

The filter media 196 may have a backing or substrate 200 that mayprovide support to the primary filter media 196. The backing orsubstrate 200 may be made of paper or other porous but generally stiffmaterial so that air or other fluid may pass through, yet the substrate200 may not generally act as a filter media itself. In this regard, thesubstrate 200 should then have a collection size (that is a sufficientlyporous structure) such that the substrate 200 serves to collect onlyparticles that are larger, and not smaller, than those particlescollected by the primary filter media 196.

The filter media 196 may also be a thin plastic film which is borne upona substrate like paper, measure plastic or otherwise that selectivelytraps or holds back particles above a certain size. Whether the filtermedia 196 is a thin plastic film, a paper or fiber based filtermaterial, or otherwise, the filter media 196 is permeable or porous toallow fluid and/or airflow through it yet selectively captures particlesaccording to size on the filter membrane. The filter media may be usedin conjunction with or in the place of a glass slide, sticky media orotherwise with respect to the sample plate 140.

Note should be taken, that the sample plate 140 generally does not inany way contact any of the side ledges, supports, and/or spacers 154that intermittently circumscribe the perimeter of the bottom 156 of thebottom cover 104. This is to prevent any compression upon the slide 140or to otherwise have the bottom cover 104 interfere with the operationof the sample plate 140.

Sample plate 140 is generally retained along the central rib 172 byadhesive 192 which is generally adhesive enough to provide stability forthe sample plate 140 yet allows removal of the sample plate 140 from thetop cover 102 to analyze the sample taken by the sample plate 140. Thespacing support ledges 176 serve to help position and stabilize thesample plate 140. To provide additional stability and to direct airflowfor filter media 196 sample plates 140, the gaps 142 shown in FIGS. 4and 5 may be omitted with the filter media spanning the entire width ofthe bottom 130 of the top cover 102. This forces all air or other fluidthrough the filter media 196 to ensure collection of as much particulatematter as possible.

In such a case, the junction between the filter media 196 as a part of asample plate 140 and the spacing support ledge 176 would be complete asshown in FIG. 3 around the entire perimeter of the filter media sampleplate 140.

The collecting slide 140 may be temporarily fixed with a tacky materialto the center cross support rib 172. The collecting slide 140 may becoded (as, for example, with etched letters “A” and “B”) to uniquelycorrespond to similarly marked inlets (“A” and “B”) in order topermanently identify the samples.

As partially shown in Figures, four or possibly more side ledges 154extend upwardly from the base 104. Note should be taken that the sampleplate 140 does not rest in any way upon the ledges 154. Instead, thecentral posts 136 as well as the circumscribing sidewall 132 are theportions of the top cover 102 which engage such ledges 154. In fact,generally, these are the only structures that do engage the side ledges154.

The presence of the central rib 172 with its adhesive 192 enables thecassette 100 to be used in conjunction with a variety of differentsample plates 140. While the cassette 100 may be disposable in nature,its useful life may extend far beyond that of a single use (or a dividedsingle use if each of the two inlets 110, 112 are used at separatetimes).

By selecting an advantageous adhesive, a variety of sample plates 140 inthe form of glass slides, plates, filter media, combinations thereof andthe like of a variety of collection sizes and characteristics may beused to good effect. Advantageous selection of the adhesive 192 enablesthe detachable attachment of the sample plate 140 to the central rib172. The spacing support ledges 176 of the top cover 102 then serve toprovide lateral support for the sample plate 140 which would otherwisebe able to rock back and forth much like a seesaw or teeter-totter aboutthe central rib 172. The spacing support ledges 176 eliminate thisdegree of freedom for the sample plate 140 and prevents any rockingabout the axis defined by the central rib 172. The central rib 172itself prevents any rocking motion along an axis perpendicular to thecentral rib 172.

While multiple uses of the cassette 100 may require separateapplications of adhesive 192, such applications are not seen asproviding any significant contamination for the cassette should it beused in an otherwise clean environment. Under some circumstances, apristine cassette 100 may be desirable and the cassette 100 may besubject to only a single use.

A disposable filter screen may be used in conjunction with the cassette100 including filter screens with selectable openings ranging from 5 μmto 300 μm. Such a disposable filter screen may be fitted onto an inletor fitted onto a separate attachment such as a collection hose fortransmission of air samples to the cassette 100. Filtration preventslarge particles and debris from entering the selected inlet and it alsoallows for particles of a known size only to be sampled.

The integrity of the samples gathered by the sample plate 140 may bemaintained by using plastic caps fitted onto the inlet 110, 112 and exit152 ports. This keeps an unused cassette clean prior to sampling andwhen one side is in use, the other sample chamber is protected fromcontamination or inadvertent use. Furthermore, the plastic caps preventa used cassette from being contaminated after a sample has beencollected.

As shown in FIGS. 6 and 7, caps of a variety of types and characteristicmay be used.

In FIG. 6, a first flat and sealingly covering cap 220 is shown affixedto the top cover 102 on the right inlet 112. The closed cap 220 hascircumscribing walls 222 that in a generally sealingly engaging mannercover the inlet 112 and prevent fluid or airflow past the cap 220 andinto the interior 118 of the inlet 112. The gap 220 may have a tab 224that allows for easy manual engagement of the cap 220, allowing it to beeasily removed from and replaced on the inlet 112. The cap 220 may bemade of polypropylene or other material and is preferably soft so thatit sealingly engages the top 116 of the inlet 112.

Also in FIG. 6, a second type of cap, a filter cap 230, is shown thatalso has circumscribing walls 222 that generally sealingly engage theinlet 110 (as shown in FIG. 6) by sealingly engaging the inlet top 116and preventing a passage of air or other fluid into the interior 118 ofthe inlet 110. Both types of caps can be of any shape and/or size

The filter cap 230 may also have a tab 224 for lifting and replacing thecap 230 from and on the inlet 110. As shown in FIG. 6, the filter cap230 has a top mesh 232 that allows for the passage of air into andthrough the cap 230. The top mesh holds in compression or otherwisefilter media 234 that may be similar to or different from the filtermedia 196 used in the sample plate 140. The filter media 234 may begenerally entrapped by a second mesh (not shown) that resides within theinterior of the filter cap 230 below the filter.

The filter media may act as a pre-filter to exclude particles largerthan a certain particle size that may be present in the surrounding areawhen collection is made of an air sample. The resulting air passing intothe interior 118 of the inlet 110 is then pre-filtered to exclude suchlarger particles. If a filter media 196 is used in conjunction with oras the sample plate 140, such filter media 196 may collect particles ofa smaller size, enabling even smaller particles to go through. As aresult, it would be possible (for example) to exclude sawdust in a dustysawmill but still sample the air for pollen or the like as sawdustparticles are generally very large while pollen particles would be ableto pass through the filter cap 230 with its top mesh 232, through thefilter media 234 and onto the sample plate 140.

If the sample plate is a glass slide with or without sticky media, theair flowing past the sample plate 140 would also be sampled for itsparticulate matter. Due to the nature of the sticky or other media,different materials or particles according to different sizes may becollected. Operation of the inlets 110, 112 with respect to theselection of particle size may generally not be affected by the presenceor absence of a filter cap 230.

In FIG. 7, the capped dual air particle sample cassette 100 of FIG. 6 isshown in a sealed condition of the type normally presented to the enduser of the cassette. Circumscribing tape 240 circumscribes the seam 242(FIG. 6) present between the top cover 102 and the bottom cover 104 ofthe cassette 100. Lateral tapes 244 hold in place and maintain the sealprovided by the caps 220, 234 in the example shown in FIG. 7. In orderto seal the filter cap 230, a thin plastic or other obstructing sheetmay be present underneath the lateral tape 244 holding the filter cap230 in place. The sealing sheet (not shown) serves to seal the top mesh232 and prevent air with its accompanying particulate matter fromentering into the filter cap 230 past the top mesh 232.

Both types of tape, the circumscribing tape 240 for the seal 242 and thelateral tapes 244 for the caps 220, 230 are sufficiently adhesive andresilient to preserve the seals necessary so that samples cassettes 100are not contaminated by inadvertent introduction of unintendedparticulate matter. The adhesive attachment of the tapes 240, 244 may besuch that they may be removed generally without leaving any adhesiveresidue on the cassette 100. This prevents contamination of samples byadhesive material and generally allows the clean removal of the tapes240, 244.

The lateral tapes 244 enable the selective use of either one of theinlets 110, 112 individually, or allow them to be used simultaneously.For the exemplary embodiment shown in FIG. 7, removal of the lateraltapes 244 and removal of the closed cap 220 as well as removal of anysealing sheet for the top mesh 232 of the filter cap 230 would enabletwo samples to be taken of the same fluid, or air, with the filter cap230 pre-filtering such a sample to collect the smaller particles whilethe other side of the sample plate 140 corresponding to inlet 112 wouldreceive all of the suspended particulate matter as such air was notpre-filtered. Under such circumstances, it may be advantageous tocollect the filter media 234 of the filter cap 230 to subject it totesting.

The circumscribing seam sealing tape 240 may be removed upon delivery ofthe cassette 100 to a laboratory or other testing facility so that thesample plate 140 may be collected and analyzed.

While the present invention has been described with regards toparticular embodiments, it is recognized that additional variations ofthe present invention may be devised without departing from theinventive concept.

1. A method of obtaining multiple air samples using a single airsampling device, said air sampling device comprising a cassetteincluding a first inlet and a second inlet, the method comprising: a)drawing a first sample of air through said first inlet, while the secondinlet is covered by a removable cap; b) collecting particulatescontained in said first sample of air on a first collection structure;c) removing said cap from said second inlet: d) drawing a second sampleof air through second inlet, while said first inlet is covered by aremovable cap; e) collecting particulates contained in said secondsample of air on a second collection structure; wherein the secondsample of air is prevented from commingling with the particulatescollected from said first sample of air prior to contact with the secondcollection structure; f) drawing said first sample of air past saidfirst collection structure and out of said cassette through an outlet;and g) drawing said second sample of air past said second collectionstructure and out of said cassette through said outlet; wherein steps a)and d) occur sequentially.
 2. The method as recited in claim 1, whereinsteps a) and b) occur in a different location than steps d) and e). 3.The method as recited in claim 1, wherein steps a) and b) occur in asame location as steps d) and e).
 4. The method as recited in claim 1,wherein said first collection structure comprises a portion of a sampleslide disposed in said cassette for performing the collecting step b).5. The method as recited in claim 4, wherein a different portion of saidsample slide comprises the second collection structure for performingthe collecting step e).
 6. The method as recited in claim 1, whereinboth steps b) and e) are performed without rotating any components ofsaid cassette relative to other components of said cassette.